RADIOULNAR JOINTS the Radius and Ulna Articulate by –
RADIOULNAR JOINTS The radius and ulna articulate by – • Synovial 1. Superior radioulnar joint 2. Inferior radioulnar joint • Non synovial Middle radioulnar union Superior Radioulnar Joint This articulation is a trochoid or pivot-joint between • the circumference of the head of the radius • ring formed by the radial notch of the ulna and the annular ligament. The Annular Ligament (orbicular ligament) This ligament is a strong band of fibers, which encircles the head of the radius, and retains it in contact with the radial notch of the ulna. It forms about four-fifths of the osseo- fibrous ring, and is attached to the anterior and posterior margins of the radial notch a few of its lower fibers are continued around below the cavity and form at this level a complete fibrous ring. Its upper border blends with the capsule of elbow joint while from its lower border a thin loose synovial membrane passes to be attached to the neck of the radius The superficial surface of the annular ligament is strengthened by the radial collateral ligament of the elbow, and affords origin to part of the Supinator. Its deep surface is smooth, and lined by synovial membrane, which is continuous with that of the elbow-joint. Quadrate ligament A thickened band which extends from the inferior border of the annular ligament below the radial notch to the neck of the radius is known as the quadrate ligament. Movements The movements allowed in this articulation are limited to rotatory movements of the head of the radius within the ring formed by the annular ligament and the radial notch of the ulna • rotation forward being called pronation • rotation backward, supination Middle Radioulnar Union The shafts of the radius and ulna are connected by Oblique Cord and Interosseous Membrane The Oblique Cord (oblique ligament) The oblique cord is a small, flattened band, extending downward and laterally, from the lateral side of the ulnar tuberosity to the radius a little below the radial tuberosity.
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